In the manufacturing process of thin semiconductor devices, an important step is depositing a thin oxide layer to provide insulation between conductive layers. For example, a thin oxide layer is formed between a polysilicon gate electrode and the substrate underneath the gate electrode. The thin oxide layer functions as an insulating layer. The thin oxide layer may be formed by suitable fabrication techniques.
The commonly used oxide layer fabrication techniques can be divided into two categories. The first category includes a variety of film growth processes through interaction of a vapor deposited species with the top surface of a substrate. For example, a thermal oxidation process represents a typical implementation of the first category. The thermal oxidation process may further be divided into two subclasses, namely dry oxidation and wet oxidation. In a dry oxidation process, the surface of a substrate is exposed to an oxidizing ambient environment comprising pure O2, and as a result, a SiO2 layer is formed on top of the substrate through interaction between O2 and the silicon surface of the substrate. In contrast, in a wet oxidation process, the substrate is exposed to an oxidizing ambient environment comprising steam or water vapor.
The second category of oxide layer fabrication techniques may include a deposition process without causing changes to the top surface of the substrate. The second category includes a variety of suitable fabrication processes such as a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, a plasma enhanced CVD (PECVD) process and the like.
In a PECVD process, due to good conformal step coverage and gap filling characteristics, tetraethoxysilane gas (Si(OC2H5)4) is used as a source material of silicon. Tetraethoxysilane gas is commonly known as TEOS. Throughout the description, for simplicity, Tetraethoxysilane is alternatively referred to as TEOS.
According to the fabrication steps of a PECVD process, a wafer may be placed in a reaction chamber. A gas combining TEOS and other suitable process gases such as oxygen (O2), ozone (O3) or the like are fed into the reaction chamber through a manifold. In the reaction chamber, Si(OC2H5)4 reacts with O2 to generate SiO2 and corresponding byproducts. The PECVD based oxide deposition is carried out at a temperature range from about 250 degrees to about 450 degrees and a pressure level from about 2 torr to about 10 torr.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.